232 



THE ANIMALS AND MAN 



The soaring bird evidently takes advantage of horizontal air- 

 currents, and some observers maintain that upward currents 

 also must be present. The speed of flight of some birds is 

 enormous, the passenger-pigeon having been estimated to 



FIG. 124. Sickle-billed thrasher, Harporhynchus redivivus. (Photograph 

 from life by Eliz. and Jos. Grir.nell.) 



attain a speed of one hundred miles an hour. The long 

 distances covered in a single continuous flight by certain 

 birds are also extraordinary, as is also the total distance 

 covered by some of the migrants. The differences in the 

 structural character of the wings should be noted in connec- 



